1. Field of the Invention
The present invention relates generally to controls for fuel injection systems for internal combustion engines. More specifically, the invention relates to a control for regulating injection timing in fuel injectors for compression ignition type internal combustion engines, wherein fuel is supplied to unit fuel injectors which operate on a pressure-time metering principle.
2. Background Art
Unit fuel injectors which operate on a pressure-time metering principle have been in use for some time now (see U.S. Pat. Nos. 4,721,247; 4,986,472 and the patents mentioned therein), and have contributed greatly to the ability of internal combustion engine designers to meet the ever increasing demands for improved pollution control and increased fuel economy. In fuel supply systems using such injectors, fuel is supplied by a gear pump to all of the injectors via a common fuel rail and the same is true for timing fluid used to control the degree that the timing of the injection event is advanced or retarded, with the quantity of fuel and timing fluid delivered to each injector being a function of the supply pressure from the common rail and the time period during which the metering and timing chambers are in communication with the respective supply rails. Examples of gear pump type fuel supply systems for P-T type unit fuel injectors can be found in U.S. Pat. Nos. 4,909,219 and 5,042,445.
However, for the continuing demands for improved pollution control and increased fuel economy to be met, it becomes increasingly essential to be able to optimize the combustion process, not only by precisely controlling the quantity of fuel injected into each cylinder, but also by precisely regulating the timing thereof, and this has become increasingly more difficult as the level of combustion efficiency to be obtained is raised. Ultimately, increased precision means that the controller must be infinitely variable as well as responsive to the various parameters affecting fuel quantity and timing. Furthermore, since the governmental demands for emissions are less stringent for engine operation under steady-state (cruise) conditions than they are for transient (city/acceleration) conditions, increased fuel economy is obtainable if the controller can distinguish between transient and steady state operating conditions, and modify the engine timing accordingly. Ideally, such a controller would not require significant redesign of existing systems, so that it could be retrofit installed on them, not merely incorporated into new units.
U.S. Pat. No. 4,869,219 discloses an air fuel control for P-T fuel systems which uses a diaphragm-type operator to provide a controlled, optimum amount of fuel as a function of intake manifold pressure, and which can be retrofit installed on previously existing engines. However, no equivalent control for regulating engine timing is provided, nor is any delay function provided for enabling a modified effect to be produced once steady-state operation has been achieved.
U.S. Pat. Nos. 3,486,492 and 4,408,591 show fuel injection pumps which have a built-in timing control which can delay advancing of injection timing upon acceleration. However, these disclosures relate to distributor-type pumps not gear pumps, and are not adapted to the needs of P-T fuel injectors and the fuel systems therefor.